make sure you shake LIGHTLY the excess moisture off your leaves after adding anything, even plain water to em. I would get this stuff at home de pot called organicide. Smells like rotten fish, but it kills gnats, and their larvae that grow and reproduce IN the soil. Mix 1 cup per gallon.
good vibes

Or any pyrethin spray....again, make SURE to shake off excess moisture on leaves. It acts like a magnifying glass for the light to burn the leaves.